Shoot Spacing and Canopy Light Microclimate

Abstract

The light microclimate of a range of shoot densities (5 - 74 shoots/m) was measured for the cultivar Gewürztraminer. The shoots were trained vertically up or down on four different trellis systems. Theoretical analysis showed that leaf layer number (LLN) varies linearly with the ratio of leaf area to shoot length, mean leaf angle, and shoot density. Low shoot densities (< 10 shoots/m) produced open canopies with a high proportion of canopy gaps, and most leaves and fruit were well exposed to sunlight. High shoot densities (> 30 shoots/m) produced canopies with no gaps, and the majority of fruit and leaves were interior and shaded. Such canopies were characterized by low interior values of photosynthetic photon fluence rate, shortwave radiation, and red to far red ratio. A shoot density of ca 15 shoots/m appears optimal for this variety and location to maintain an adequate canopy microclimate. Closer shoot spacing causes undesirable shading, and wider spacing causes incomplete radiation interception. This paper discusses a range of canopy light measurement methods, both direct and indirect. Of the indirect methods, point quadrat analysis, visual assessment, and measurement of sunfleck length were all quick and simple and produced results related to more time-consuming direct methods with light meters.